Soft-Output Decision-Based Detection of SSK, BI-SSK and QSM

Space shift keying (SSK) modulation is a special case of conventional spatial modulation (SM), where the amplitude and/or phase modulation symbols are eliminated from the transmission process so as to reduce complexity. However, high spectral efficiencies are difficult to achieve with SSK. At the same time, the spectral efficiency of SM can be further improved. On this note, to further enhance the spectral efficiencies of both SM and SSK, quadrature SM (QSM) and Bi-SSK modulations, respectively, were proposed. In coded channels, typically soft-output detection coupled with soft-input channel decoding yields significant signal-to-noise ratio (SNR) gain. Hence, in this paper, we propose soft-output maximum-likelihood detectors (SOMLD) for SSK, Bi-SSK and QSM modulated systems. Monte Carlo simulation results demonstrate that the error performances of the proposed SOMLD schemes closely match with that of their hard-decision maximum-likelihood detector counterparts in uncoded channels; while, significant SNR gains are yielded in coded channels.